The present invention relates to reflector antennas, and more particularly, to multi-band antennas for spacecraft having frequency selective absorber surfaces or frequency selective surfaces
Spacecraft, particularly satellite communication systems, use reflector antennas to transmit and to receive microwave frequency signals, typically, to and from land based communication stations. Advanced satellite communication systems typically require low mass, low volume, low cost, multi-band antennas. Examples of multi-band antennas where the same reflector is used for both uplink and downlink frequencies, which are different, are disclosed in U.S. Pat. No. 6,169,524 B1. The multi-band antennas disclosed in this patent utilize frequency selective or polarization sensitive zones to enable a single reflector to provide the plurality of antenna patterns for the different uplink and downlink frequencies.
Some applications require that different frequency bands have the same beamwidth or beam coverage cell size. In such applications, the antenna reflector for a multi-band antenna must provide the same cell size for the different frequency bands.
A multi-band antenna reflector for use with first and second different frequency bands to produce a comparable beam cell size for each frequency band with high performance, low sidelobe and cross polarization levels, and a superior carrier-to-interference ratio (C/I) in accordance with an embodiment of the invention has a concave reflector. The concave reflector has central and outer concentric zones. The central concentric zone reflects signals in the first and second frequency bands and the outer concentric zone is configured as a frequency selective absorber that reflects signals in the first frequency band and absorbs signals in the second frequency band. The frequency selective absorber has a finite conducting pattern or lossy element pattern dimensioned to reflect signals in the first frequency band with a predetermined equivalent reactance value and absorb the signals in the second frequency band with a pre-determined sheet resistance (ohms/square) and absorber rings disposed at the periphery of the outer concentric zone.
A multi-band antenna reflector for use with first and second different frequency bands to produce a comparable beam cell size for each frequency band with high performance, low sidelobe and cross polarization levels, and a superior carrier-to-interference ratio (C/I) in accordance with another embodiment of the invention has central and outer concentric zones. The central concentric zone has a reflective layer on an inner surface that reflects signals in the first and second frequency bands. The outer concentric zone is a frequency selective surface formed of a dielectric core having a finite conducting pattern on top and bottom sides. The conductive pattern is dimensioned to reflect signals in the first frequency band and pass signals in the second frequency band. Resistance cards overlay the top and bottom of the junction between the reflective layer of the central zone and the frequency selective surface of the outer zone.
In an embodiment of the invention, dual frequency feeds transmit signals in the first and second frequency bands to the concentric zones.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.